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- [Instructor] Of course, another thing

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that you'll want to do in Python

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is be able to read the contents
of a file into your program

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for processing purposes.

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So, let's take a look at a with statement

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that opens a file for reading.

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Now, as you can see here,

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at the beginning of this with statement,

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we are once again using
the built-in open function

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to open up the accounts.txt
file that we previously created

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that had five fake bank accounts in it.

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And, in this case, we are
opening the file for reading.

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The mode r is opening a
text file for reading.

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And this open command will work

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only if the file already exists

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and can be found at
the specified location.

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Now, because I'm not
specifying a location here,

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it is going to assume the
file is in the current folder

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from which I am executing
iPython at the moment.

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So, indeed it is, as I showed
you in a preceding video.

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So we're gonna open up
that file for reading

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and we're going to assign
it to the variable accounts

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so that we can use that
in the sweep below.

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Now, let me go ahead
and execute this first

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just so you can see the results.

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As you can see, we have
three columns of information

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and we've formatted the
data in those columns

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to be left-aligned in
the first two columns

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and right-aligned in the third column.

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So first of all, we
printed the column heads

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and we only did that if the
file was opened correctly.

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If the file is not opened correctly

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because, for example,
the file doesn't exist,

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an exception would have occurred

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and the with statement would
have terminated immediately.

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So, by putting the print
statement in the with statement,

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it will be displayed
only if we successfully

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opened the file.

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Now, as you can see, we're
printing a formatted string,

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an f string.

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And in the first placeholder,

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we have the string Account
left-aligned in a field of 10.

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In the second placeholder,

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we have the string Name
left-aligned in a field of 10.

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And in the last column,

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we have the string Balance
right-aligned in a field of 10.

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And that's going to
enable us to right-align

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all of the numeric values and
line up their decimal points.

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Now, the important piece in the body

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of the with statement
here is this for loop,

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which is iterating through the
file object that we created.

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One of the interesting things
about file objects in Python

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is that they are iterable.

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And in the case of a text file,

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this automatically reads one
line at a time from the file.

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So, for each of the records in accounts,

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for each line of text in
the accounts file object,

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we are going to tell that string to split,

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which will give me a list
of the pieces of information

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which were separated by spaces

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in the actual records of text
that were written to the file

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in the first place.

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We will then unpack that list,
which has three values in it,

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into account, name, and balance

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which is the specific order

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in which each record of
information was written.

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First, we had an account number.

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Then a last name.

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Then a balance.

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And finally, we will then print
out that set of information

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for the current record

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and, once again, we're using an f string.

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So the account number will be
left-aligned in a field of 10,

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underneath the string Account.

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The name value will be
left-aligned in a field of 10,

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under the column head Name.

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And the balance value
will be right-aligned

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in a field of 10.

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And remember, these are all
string pieces of information,

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so I'm not using
floating-point formatting here.

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I'm simply redisplaying the text

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that was read from the file.

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If we had subsequently read the text

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and converted it into a numeric value,

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only then would I use numeric formatting

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in this particular case.

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Now what's going to
happen to this for loop

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is it will keep reading from the file

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until the end of file indicator

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is emitted from reading from the file.

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So that's taken care of for you

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at the operating system level,

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and, once that happens,

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the for loop automatically terminates.

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And once the for loop terminates,

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the with statement will terminate

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and automatically close
the accounts.txt file.

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Now, you may be wondering
whether you have to iterate

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one line at a time through a text file.

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It turns out that you don't.

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There is a method built
into the file object

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called read lines,

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which will read the entire text file

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and give you back a list of strings

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representing the individual
lines of text within the file.

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However, keep in mind
that if the text file

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is extremely large, that could take time

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and could take up a
lot of memory, as well.

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Whereas iterating one line at
a time through the text file

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is accessing the data
on demand, if you will,

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giving you only one string
at a time from the file,

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enabling you to process that

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and then basically forget
about it at that point

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and move on to the next record.